1. Field of the Invention
This invention relates to a process for the recovery of mercury from a mercury-contaminated material, and in particular, to a mercury-contaminated soil. The invention also relates to a process for the remediation of said soils by the removal of mercury from all or a portion of these soils.
2. Description of the Related Art
Liquid mercury is used in a variety of industrial process including its use as an electrode in some chlor-alkali plants for the production of chlorine and caustic. The use of such mercury cells for this application is well known in the industry.
Occasionally, during operation of this type of chlor-alkali plant, some mercury may be lost to the environment where it contaminates the soil in the immediate vicinity of the cell. This contaminated soil is generally disposed of by, for example, sending the soil to a suitable landfill operation which is set up to handle this type of waste material. However, since the actual amount of mercury loss to the environment is relatively small, and the amount of soil which must be land-filled is generally large, the cost of such a land-filling operation can amount to a significant expense.
In the mining industry, it is known that soil particles containing precious metals, such as gold, can be separated from other particles of comminuted ores, by use of a hydraulic mineral separator. This type of device uses a upward flow of a liquid, which is preferably water, through an essentially vertical tube, to separate those particles having a higher density from those particles with a low density. Generally, the liquid stream enters the vertical tube at or near the bottom of the tube and flows upwardly until it exits the tube at or near the top of the tube. Soil particles of an essentially constant size (by volume) are fed into the top of the tube. The rate of liquid flow is controlled so that only the heavier particles will settle and/or sink through the upwardly flowing liquid stream. The lighter particles are unable to sink through the upwardly flowing liquid stream and remain at, or near the top of the vertical tube.
These types of hydraulic mineral separators have been know for a number of years and have been described by, for example Miller in U.S. Pat. No. 1,483,371 (issued Feb. 12, 1924), McDaniel et al. in U.S. Pat. No. 3,642,129 (issued Feb. 15, 1972), Turbitt et al. in U.S. Pat. No. 4,554,066 (issued Nov. 19, 1985), and Kuryluk in U.S. Pat. No. 4,789,464 (issued Dec. 6, 1988). While these types of devices have been known for several years, their primary use has been limited to the classification of ore samples for mining operations as a guide to the amount of heavy metals present in an ore sample. To date, it has been unknown to use an hydraulic mineral separator for the purpose of recovering mercury from a mercury-contaminated material, or for recovering mercury or other heavy metals (or concentrating into a smaller soil sample) from heavy metal-contaminated soils.